Odds are you sometimes think about calories. They are among the most often counted things in the universe. When the calorie was originally conceived it was in the context of human work. More calories meant more capacity for work, more chemical fire with which to get the job done, coal in the human stove. Fat, it has been estimated, has nine calories per gram, whereas carbohydrates and proteins have just four; fiber is sometimes counted separately and gets awarded a piddling two. Every box of every food you have ever bought is labeled based on these estimates; too bad then that they are so often wrong.
A Food is Not a Food—Estimates of the number of calories in different kinds of foods measure the average number of calories we could get from those foods based only on the proportions of fat, carbohydrates, protein and sometimes fiber they contain (In essence, calories ingested minus calories egested). A variety of standard systems exist, all of which derive from the original developed by Wilbur Atwater more than a hundred years ago. They are all systems of averages. No food is average.
Differences exist even within a given kind of food. Take, for example, cooked vegetables. Cell walls in some plants are tougher to break down than those in others; nature, of course, varies in everything. If the plant material we eat has more of its cell walls broken down we get more calories from it. In some plants, cooking ruptures most cell walls; in others, such as cassava, cell walls hold strong and hoard their precious calories in such a way that many of them pass through our bodies intact.
It is not just cooked vegetables though. Nuts flagrantly do their own thing, which might be expected given that nuts are really seeds whose mothers are invested in having them escape digestion. Peanuts, pistachios and almonds all seem to be less completely digested than their levels of protein, fat, carbohydrates and fiber would suggest. How much? Just this month, a new study by Janet Novotny and colleagues at the USDA found that when the “average” person eats almonds she receives just 128 calories per serving rather than the 170 calories “on the label.”
It is not totally clear why nuts such as almonds or pistachios yield fewer calories than they “should.” Tough cell walls? Maybe. But there are other options too, if not for the nuts themselves then for other foods. (...)
In general, it seems that the more processed foods are the more they actually give us the number of calories we see on the box, bag or other sort of label. This applies not just to cooking and pounding but also to industrial processing. A new study this year found that in a lab experiment individual humans who ate 600 or 800 calorie portions of whole wheat bread (with nuts and seeds on it) and cheddar cheese actually expended twice as much energy, yes twice, in digesting that food as did individuals who consumed the same quantity of white bread and “processed cheese product.” As a consequence, the net number of calories the whole food eaters received was ten percent less than the number received by the processed food eaters (because they spent some of their calories during digestion). Similar work in pythons has shown that cooked and/or ground up meat also requires less energy to digest (at least for pythons). If you want more calories, whether or not you are a snake, cook, pound and otherwise predigest your food.
A Body is Not a Body—Amazingly, there are more ways in which a calorie is not a calorie. Even if two people were to somehow eat the same sweet potato cooked the same way they would not get the same number of calories. Carmody and colleagues studied a single strain of heavily inbred lab mice such that their mice were as similar to each other as possible. Yet the mice still varied in terms of how much they grew or shrank on a given diet, thanks presumably to subtle differences in their behavior or bodies. Humans vary in nearly all traits, whether height, skin color, or our guts. Back when it was the craze to measure such variety European scientists discovered that Russian intestines are about five feet longer than those of, say, Italians. This means that those Russians eating the same amount of food as the Italians likely get more out of it. Just why the Russians had (or have) longer intestines is an open question. Surely other peoples differ in their intestines too; intestines need more study, though I am not going to volunteer to do the dirty work. We also vary in terms of how much of particular enzymes we produce; the descendents of peoples who consumed lots of starchy food tend to produce more amylase, the enzyme that breaks down starch. Then there is the enzyme our bodies use to digest the lactose in milk, lactase. Many (some say most) adults are lactose deficient; they do not produce lactase and so do not break down the lactose in milk. As a result, even if they drink milk they receive far fewer calories from doing so than do individuals who produce lactase. Each of us gets a different number of calories out of identical foods because of who we are and who our ancestors were.
A Food is Not a Food—Estimates of the number of calories in different kinds of foods measure the average number of calories we could get from those foods based only on the proportions of fat, carbohydrates, protein and sometimes fiber they contain (In essence, calories ingested minus calories egested). A variety of standard systems exist, all of which derive from the original developed by Wilbur Atwater more than a hundred years ago. They are all systems of averages. No food is average.Differences exist even within a given kind of food. Take, for example, cooked vegetables. Cell walls in some plants are tougher to break down than those in others; nature, of course, varies in everything. If the plant material we eat has more of its cell walls broken down we get more calories from it. In some plants, cooking ruptures most cell walls; in others, such as cassava, cell walls hold strong and hoard their precious calories in such a way that many of them pass through our bodies intact.
It is not just cooked vegetables though. Nuts flagrantly do their own thing, which might be expected given that nuts are really seeds whose mothers are invested in having them escape digestion. Peanuts, pistachios and almonds all seem to be less completely digested than their levels of protein, fat, carbohydrates and fiber would suggest. How much? Just this month, a new study by Janet Novotny and colleagues at the USDA found that when the “average” person eats almonds she receives just 128 calories per serving rather than the 170 calories “on the label.”
It is not totally clear why nuts such as almonds or pistachios yield fewer calories than they “should.” Tough cell walls? Maybe. But there are other options too, if not for the nuts themselves then for other foods. (...)
In general, it seems that the more processed foods are the more they actually give us the number of calories we see on the box, bag or other sort of label. This applies not just to cooking and pounding but also to industrial processing. A new study this year found that in a lab experiment individual humans who ate 600 or 800 calorie portions of whole wheat bread (with nuts and seeds on it) and cheddar cheese actually expended twice as much energy, yes twice, in digesting that food as did individuals who consumed the same quantity of white bread and “processed cheese product.” As a consequence, the net number of calories the whole food eaters received was ten percent less than the number received by the processed food eaters (because they spent some of their calories during digestion). Similar work in pythons has shown that cooked and/or ground up meat also requires less energy to digest (at least for pythons). If you want more calories, whether or not you are a snake, cook, pound and otherwise predigest your food.
A Body is Not a Body—Amazingly, there are more ways in which a calorie is not a calorie. Even if two people were to somehow eat the same sweet potato cooked the same way they would not get the same number of calories. Carmody and colleagues studied a single strain of heavily inbred lab mice such that their mice were as similar to each other as possible. Yet the mice still varied in terms of how much they grew or shrank on a given diet, thanks presumably to subtle differences in their behavior or bodies. Humans vary in nearly all traits, whether height, skin color, or our guts. Back when it was the craze to measure such variety European scientists discovered that Russian intestines are about five feet longer than those of, say, Italians. This means that those Russians eating the same amount of food as the Italians likely get more out of it. Just why the Russians had (or have) longer intestines is an open question. Surely other peoples differ in their intestines too; intestines need more study, though I am not going to volunteer to do the dirty work. We also vary in terms of how much of particular enzymes we produce; the descendents of peoples who consumed lots of starchy food tend to produce more amylase, the enzyme that breaks down starch. Then there is the enzyme our bodies use to digest the lactose in milk, lactase. Many (some say most) adults are lactose deficient; they do not produce lactase and so do not break down the lactose in milk. As a result, even if they drink milk they receive far fewer calories from doing so than do individuals who produce lactase. Each of us gets a different number of calories out of identical foods because of who we are and who our ancestors were.
